Gas phase 11Σu+ ← X1 Σg+ electronic spectra of polyacetylenes HC 2nH, n = 5-7

Abstract

The 11Σu+ ← X1 Σg+ system in polyacetylenes HC2nH (n = 5-7) has been observed for the first time in the gas phase. The UV absorption spectra of these chains were recorded using the resonant two-color two-photon ionization technique. A strong vibrational progression corresponding to the acetylenic stretching mode in the excited state has been observed. The absorption energy showed an inverse dependence on the chain length. The relaxation process of the 11Σu+ excited state has been discussed. © 2009 American Chemical Society.